Both had been due to arrive in the UK this week to spend time with the royals ahead of Saturday, including the Queen, the Duke of Edinburgh, the Prince of Wales, the Duchess of Cornwall, and the Duke and Duchess of Cambridge.

Video:Meghan Markle's dad reportedly 'wants to walk her down aisle' but is 'in hospital'

Ms Ragland, a yoga instructor and social worker who met Prince Harry at the Invictus Games in Toronto last year, was whisked through security at Heathrow's VIP Windsor suite after her 10-and-a-half-hour flight from Los Angeles, where she lives.

She was met by Ms Markle's personal assistant, Amy Pickerill, while Prince Harry's aides were seen helping with her luggage, including the Burberry garment bag she was spotted carrying out of her LA home on Tuesday.

The future royal mother-in-law is believed to have left Heathrow in a Jaguar estate, which is part of the royal fleet, accompanied by police cars.

She is expected to have been taken to see her daughter and future son-in-law before meeting other members of the royal for the first time before the wedding.

Image:Security personnel helped Ms Ragland with her luggage and took her to LAX

The likely absence of Mr Markle, 73, was first reported on Monday by TMZ, which said he had decided not to appear after being left "deeply embarrassed" by the release of pictures that appeared to show him colluding with photographers.

:: Sky News will broadcast live in Windsor the week before the royal wedding with all the build-up to the big day, with exclusive live coverage of the wedding in UHD in a special programme ‪from 9am to 3pm on Sky News and Sky One ‪on Saturday 19 May.